Flow separation generally occurs when a boundary layer travels from a leading edge of a lifting surface and far enough against an adverse pressure gradient that a speed of the boundary layer relative to the lifting surface falls almost to zero. Fluid flow may become detached from the lifting surface, and instead form eddies and vortices. In aerodynamics, flow separation can often result in increased drag and reduced lift. Flow separation generally deteriorates low speed performance by causing boundary layer separation at high angles of attack. Deteriorated low speed performance in turn increases a “stall speed” of the lifting surface and potentially causes non-optimal flight conditions when the lifting surface is operating at low speed flight associated with takeoff and approach to landing.
Deployable vortex generators extend during low speed flight to keep the flow attached, but retract during cruise flight to reduce flow separation. Prior art deployable vortex generators, such as that disclosed in U.S. Pat. No. 8,087,617, require wires and actuators that add cost and weight, negating most of the benefit of retracting.